1. Field of the Invention
This invention relates to a power feed control circuit for an on-vehicle electronic control apparatus which is fed with power through a power source relay from an on-vehicle battery. More particularly, it relates to improvements in a power feed control circuit for a plurality of on-vehicle electronic control apparatuses, for example, an engine control apparatus and a transmission control apparatus, which are relevant to each other.
2. Description of the Related Art
In each of various on-vehicle electronic control apparatuses such as an engine control apparatus in which an ignition control and a fuel injection control are chiefly performed, an electronic throttle control apparatus in which the valve opening degree of a suction throttle is controlled by an electric motor in response to the trodden degree of an accelerator pedal, a transmission control apparatus in which a speed change stage is variably controlled in response to the trodden degree of an accelerator pedal and a vehicle speed, a braking control apparatus which is operated in response to the trodden degree of a brake pedal and axle pulses, and an apparatus which monitors car-outside surroundings by a monitor camera, it is general that, for the purpose of suppressing the electrical leakage of an on-vehicle battery in a parking condition or performing a fail-safe control, a power source relay having an output contact which is driven by an electromagnetic coil is used so as to feed power from the on-vehicle battery to the on-vehicle electronic control apparatus through the output contact of the power source relay.
Especially in an on-vehicle electronic control apparatus which includes a microprocessor having the functions of driving actuators that need to be subjected to origin return processing before the start of running, and storing and saving learnt data and detected abnormality information during the running, in a nonvolatile data memory at the end of the running, the electromagnetic coil of the power source relay is energized upon the closure of a power source switch, and once it has been energized, the power source relay performs a self-holding operation even after the opening of the power source switch. Further, the power source relay is deenergized after save operations such as the origin returns and the data save have been completed.
By way of example, Patent Document 1 (JP-A-5-18315, FIG. 1 and Abstract) entitled “Engine Control Apparatus for Automobile” discloses a technique wherein a power source relay which starts its operation upon the closure of a power source switch is self-held by the normality signal of a watchdog timer even after the opening of the power source switch, and a microprocessor (CPU) is stopped after the completions of the initialize operations of actuators, to stop a watchdog signal for the watchdog timer and to release the self-holding of the power source relay, whereby the delayed cutoff of the power source relay is simplified.
Besides, Patent Document 2 (JP-A-2002-323902, FIG. 1 and Abstract) entitled “Electronic Control Apparatus” discloses a technique wherein the self-holding operation of a power source relay is performed in accordance with the control output signal of a microprocessor (microcomputer), and the control output signal is stopped when the abnormality of a sum check for a program memory has occurred or when the microprocessor has been reset due to the abnormality of a watchdog signal, whereby the self-holding operation is released.
Further, in relation to this invention, Patent Document 3 (JP-A-2002-235598, FIG. 1 and Abstract) entitled “Vehicular Control Apparatus” discloses an example wherein, in an on-vehicle electronic equipment which is fed with power from an on-vehicle battery through a power source relay, a load relay which is energized and controlled by a microprocessor within the on-vehicle electronic equipment is conjointly used, and many of a group of on-vehicle electric loads are fed with powers through the output contact of the power source relay, while a specified on-vehicle electric load is fed with power from the on-vehicle battery through the output contact of the load relay, whereby the partial charges of the loads are allotted to the output contacts.
According to any of the on-vehicle electronic control apparatuses stated in Patent Documents 1 to 3, the power source relay which performs the self-holding operation upon the closure of the power source switch is included, and the self-holding operation is performed in accordance with the control output signal of the microprocessor or the normal operation signal of the watchdog timer. In any case, however, one power source relay is used for the single on-vehicle electronic control apparatus. Accordingly, a plurality of power source relays and a plurality of energization control circuits for the power source relays are required in a plurality of on-vehicle electronic control apparatuses which are relevant to each other. This poses, not only the problem that the setup is uneconomical, but also the problem that the general management of the power source relays cannot be performed.